To attract butterflies and moths to my new trap, I make a mixture of bananas and sugar and then let it fermet for a day or two before using it as bait. Today, I noticed my latest bait, after being in a metal coffee can covered by a paper towel, is moldy and I had to discard it. I have two questions: 1) How do I prevent mold in the fermenting bait and (2) why did it get moldy in the first place?

With my hornet traps, I use sugar water, a banana peel, and a little bit of white vinegar. Doesn't dissuade the wasps, so figured I'd go ahead and add a little of the vinegar to my butterfly bait. Thanks for the info.

I am guessing it was ctron himself that cares about the mold, not butterflies. I have seen butterfly food with mold at zoo/museum and butterflies take it in just fine (in the wild, mold on their food is hard to avoid and butterflies likely evolved to live with mold)._________________Selling my Canon FD 200mm F/2.8 lens